A method for manufacturing micro-mechanical acceleration sensors, in which a vibration reed is etched out of a two-layer supporting material in the top layer, is described in German Patent Application No. 40 00 903. While the substrate arranged below the flexural reed is being etched, an electric potential is applied across sections of the top layer to protect the flexural reed from being etched thereby enabling the flexural reed to be undercut.
PCT International Publication No. WO 91/03074 describes a method for introducing trenches into a semiconductor surface and for covering the side walls of these trenches with a silicon oxide. The trench bottoms are not covered with oxide and are, thus, used as starting points for undercutting the structures formed by the trenches.
A method for undercutting silicon structures by anodization is described in the article by Langet al., "Application of Porous Silicon as a Sacrificial Layer," The 7th International Conference on Solid-State Sensors and Actuators, pp. 202-204 (June 1993).
Unfortunately, the above-mentioned methods of undercutting are not necessarily compatible with other processes used in fabricating semiconductor electronics. Thus, there exists a need for a method of undercutting that is compatible with other semiconductor fabrication processes.